For some years now and even currently, various apparatuses have been used in the field of the chopping and dehydration of food waste, for the separation of the solid phase.
These apparatuses are positioned downstream of the group which effects the chopping of food waste and separate the finely dry chopped solid part from the wet chopped food waste fed in the fluid state.
In general, some more widely-used techniques can be found that can be divided into two main types.
A first type is that of so-called “press separators”. These press separators comprise a screw-feeder or screw that is rotated inside a fixed cylinder with perforated walls, in turn positioned inside an outer container to receive and contain the squeezed and separated water.
Said screw feeder receives the wet chopped food waste material, fed in the fluid state by means of a lower opening formed inside said cylinder with perforated walls, and pushes it causing it to move and advance upwards.
A truncated-conical head is positioned in the upper part of the cylinder, which is held in position by means of a spring which creates an adequate pressure in the cylinder on the advancing food waste, selectively freeing a discharge opening.
In this way, the screw feeder, cooperating with the above-mentioned truncated-conical head, rotating inside the cylinder, squeezes the food waste, eliminating the liquid part, which is normally predominant, of said waste through the holes on the walls of the cylinder.
This liquid part therefore moves into the outer container mentioned above, which receives and holds the squeezed and separated water before sending it for discharge. In practice, the water is squeezed through the rotation of the screw feeder and, in order to facilitate its discharge and keep the outer container clean, washing nozzles are positioned and directed towards the outer surfaces of the walls of the perforated cylinder that remove solid residues that have exited with the squeezing.
The squeezed portion of food waste material, on the other hand, is pushed by the screw feeder rotating upwards, towards the discharge opening inside a specific collection container for the squeezed waste material, to be recovered, treated and adequately used.
A second known and used type is that of so-called “coaxial-centrifuge separators”.
Also in this second type of separator, the two main elements, screw feeder and cylinder with perforated walls, are present but, in this case, they are both rotated.
It should be noted that the rotation rates of the two elements are generally slightly different and the cylinder with perforated walls usually rotates at a higher speed than the screw feeder.
In this second type of separating apparatus, the elimination of the liquid part squeezed from the wet food waste material in the fluid state contained therein, takes place by means of centrifugal force, again through the perforated walls of the cylinder which is also rotating, as mentioned above. Also in this case, the squeezed and centrifuged water is collected inside an outer container or carter, before being sent to the outside of the liquid separating apparatus.
An outer container receives and contains the squeezed and separated water and is equipped with washing nozzles, positioned in its interior, directed towards the outer surfaces of the walls of the perforated cylinder, to keep them clean. Consequently, inside the container there are nozzles and relative pipes which feed them with washing water.
At the same time, the squeezed part of the food waste material, pushed upwards by the rotating screw feeder, exits from a discharge opening and is collected in a specific container.
It should also be pointed out that both of these main known solutions have operative limitations mainly connected to cleaning the apparatus of the organic residues deriving from the squeezing which, in some way, are not eliminated from the screw feeder and penetrate the outer container to a certain extent. It is in fact important to avoid problems of hygiene and odors due to the residence of an easily perishable material such as waste food material which is deposited, even if in small quantities.
Centrifuge separators are at present the most advantageous solution from this point of view, as they are considered as being self-cleaning.
Press separators, on the other hand, require the daily dismantling of the screw for cleaning, which is obviously quite complicated and not a particularly pleasant activity.
As already mentioned, in both solutions, a series of nozzles are envisaged inside the container or containment carter, which produce water jets that vigorously hit the outer wall of the perforated cylinder removing the deposits of food remaining thereon.
This set of nozzles and pipes connecting them, however, represent an obstacle for the free flow of the filtered water towards the outside. Consequently, with time, they are sources of retention of residual organic material dispersed in the squeezed water.
Furthermore, it is immediately evident that inside the container or containment carter of the screw feeder/perforated cylinder group of centrifuge separators, there are areas in which the self-cleaning operation is difficult, residues remain deposited and this is also a significant limitation to the good hygiene of the whole apparatus.